Abstract: CONTEXT: Optimal ages of breast cancer screening cessation remain uncertain. OBJECTIVE: To evaluate screening policies based on age and quartiles of life expectancy (LE). DESIGN AND POPULATION: We used a stochastic model with proxies of age-dependent biology to evaluate the incremental U.S. societal costs and benefits of biennial screening from age 50 until age 70, 79, or lifetime. MAIN OUTCOME MEASURES: Discounted incremental costs per life years saved (LYS). RESULTS: Lifetime screening is expensive (151,434 dollars per LYS) if women have treatment and survival comparable to clinical trials (idealized); stopping at age 79 costs 82,063 dollars per LYS. This latter result corresponds to costs associated with an LE of 9.5 years at age 79, a value expected for 75% of 79-year-olds, about 50% of 80-year-olds, and 25% of 85-year-olds. Using actual treatment and survival patterns, screening benefits are greater, and lifetime screening of all women might be considered (114,905 dollars per LYS), especially for women in the top 25% of LE for their age (50,643 dollars per LYS, life expectancy of approximately 7 years at age 90). CONCLUSIONS: If all women receive idealized treatment, the benefits of mammography beyond age 79 are too low relative to their costs to justify continued screening. However, if treatment is not ideal, extending screening beyond age 79 could be considered, especially for women in the top 25% of life expectancy for their age.